Curiosity
by Leda74
Summary: There's a cat on board. This is no ordinary cat, however, and things are about to get worse, because the TARDIS is feeling neglected...
1. Chapter 1

Donna had just managed to close her fingers on the object under her bed when the door banged back and the Doctor barged in, shouting something. The result of this was that she recoiled, smacked her head on the underside of the bed, said an extremely impolite word and surfaced like a wounded killer whale, her face flushed.

"_What?_" she said, venomously.

"I said," the Doctor repeated, exasperated, "there's a cat in here somewhere."

"I know," said Donna, and held up the item she'd retrieved from under her bed. It was a bright green catnip mouse with only one ear. It was beginning to dawn on her that the mouse was also slightly damp, and she carefully adjusted her grip so that she was holding it by the tail instead.

"It's a little tabby and white cat," said the Doctor vaguely, seemingly hypnotised by the dangling toy. Donna snorted, dropped it and planted her hands on her hips.

"We're about forty million light years from the nearest galaxy," she said, slowly and carefully. "and we don't even have a cat flap, unless I've missed it. D'you want to tell me how it got in here?"

The Doctor didn't answer her immediately. He pulled out his screwdriver and tapped it thoughtfully against his cheek for a second, then dropped to his knees and aimed it under the bed. Blue light stuttered.

"Not sure," he said, eventually, still frowning, preoccupied with his task. "Normally I'd have assumed it sneaked on board when we stopped for pizza last night, but there aren't any cats on Karagon."

"So what eats the mice?" asked Donna. The Doctor looked shifty.

"Best if you don't ask," he said, "especially if you enjoyed the pizza." He paused, saw her expression and grinned. "It was a joke, okay? A _joke?_"

She watched the Doctor edge himself further under her bed, still scanning furiously, until he'd half disappeared. In an effort to avoid looking at his rear end, she turned towards the half open bedroom door and saw a cat. It licked its nose but made no further move.

"Doctor?" she quavered.

"_What?_" came the muffled, vaguely put-upon reply.

"Did you say you saw a tabby?"

"Yes," said the Doctor, and only now was there a thoughtful pause. "Why?" he asked.

"Well, there's a white one here," whispered Donna, her gaze still locked on that thirty per cent of cat that could be seen through the door.

"Don't take your eyes off it," said the Doctor quietly, emerging from under the bed and brushing smears of dust out of his hair. "See if you can get it in the room."

Nodding, Donna bent and clicked her fingers at the cat.

"Here, puss-puss," she said brightly, trying not to feel like an idiot. The cat merely looked her up and down with insolent yellow eyes that carried far more scorn than any animal ought to be able to muster, then turned and stalked away.

Donna raced for the door, yanked it back and stuck her head out into the corridor just in time to see a long tail disappearing around the corner. It was grey.

She pulled her head back into the bedroom, fixed the Doctor with an uncertain look and said, "Um..."

* * *

It was several minutes later, and they had arrived in the Garden of Artemis in pursuit of their quarry before losing it amongst the undergrowth. Donna sat on a wrought iron bench, got her breath back and watched the Doctor pace back and forth.

"What's a Schrödinger Cat?" she asked, puzzled.

"I'll explain the details later," he said, jamming his hands into his pockets and rocking back on his heels. "For now, let's just stick with the basic premise that these little buggers can travel in time and space and change colour whenever you're not looking at them, and if you feed them after midnight, they...no, sorry, that's Mogwai, isn't it?"

Donna stared.

"Oh," added the Doctor, "and did I mention we should worry about this, because sooner or later, where you've got one, you'll get more."

It was the first time that Donna had seen the Garden of Artemis. It wasn't what she'd have expected. The garden was a riot of clashing flora, from tall plumes of pink pampas grass to hectic beds of lupins in every conceivable colour. Hanging baskets sprouted threatening clusters of dewy Venus fly traps, and there was a rather tacky stone wheelbarrow full of white geraniums. In and amongst this garish panoply were the statues that gave the garden its name; wide-shouldered, stern female archers in various states of dress and undress, most with sleek hunting dogs at their heels.

Donna was starting to get a headache just from looking at it all. She glanced up, and her jaw dropped. Above her there was a soft orange sky, shading to ochre at the horizons, with two perfect silver suns sailing in it.

"It's a projection of the dawn on Gallifrey," said the Doctor, emerging from a nearby rhododendron bush and brushing off his hands. "It's not real. It's a memory. Mine, actually. This was how the sky looked the day that..." He stopped, and looked away. Donna, not by nature one of the world's more tactful people, quite uncharacteristically bit her lip and said nothing.

"Anyway," the Doctor went on, a shade too briskly, "no cat here. I suggest we check the Archives next."

Donna trotted after him as he loped off down a rather tasteless orange gravel pathway, shoulders hunched.

"So where do these cats come from?" she asked, drawing level.

"Schrödingers are a subspecies of your basic natural Earth cat," he explained. "They were first recorded during the Middle Ages, and the theory's that in response to the pressure of natural selection at the time, some of them developed certain quantum powers like time travel, phase shift and teleportation."

"Why," said Donna, slightly out of breath from running to keep up with the Doctor's lengthy strides, "what happened in the Middle Ages?"

"Dear me, where were you during history class, Donna Noble?" he said disparagingly, looking down at her for a second. "Witch trials and inquisitions, that's what happened. Cats became hated and feared as the minions of Satan, that's what happened!"

The Doctor was so intent on his speech that Donna was the first to notice what was amiss with their surroundings. She stopped by a very familiar stone wheelbarrow full of white geraniums and cleared her throat nervously. The Doctor pulled up sharp and gave her a quizzical glance.

"I'm not an expert," she said carefully, "but weren't we here just here a minute ago?"

"Yeah," he said, distractedly, running hand through his hair. "I think..."

Whatever he had been about to say was lost in a violent cacophony of shrieks. A small cat darted out of a shrubbery, eyes wild with terror, and zig-zagged across the clearing with its ears laid flat. Donna had barely had time to register this when a rolling tide of felinity crashed out of the same shrubbery and skimmed off in pursuit.

The Doctor, caught in this unexpected rip tide of fur, pranced around on one leg for several precarious seconds while grabbing for equilibrium with both hands, and managed to regain his composure just as the last stragglers pelted past his ankles. This achieved, he glared at Donna – who was laughing so hard that she had to hang onto a nearby statue – and sprinted after the cats.

He was back just a few seconds later. He tripped over the wheelbarrow, struggled for balance once more and, this time, failed spectacularly. Donna helped him clamber out of a tangle of squashed lupins and picked a petal off his lapel.

"Did you see them come through here?" he asked, irritably. Donna shook her head.

"No, just you," she said. "How did you manage to come from that direction?"

He didn't respond immediately, but when he did, he sounded annoyed.

"Using pockets is _naughty_," he said, severely. "What did I tell you last time? You can't keep them, okay? Now let us out! Yes?" he said, this last to Donna, who had tugged at his sleeve.

"Who are you talking to?" she asked.

"The TARDIS, of course," he said, as if this fact should have been apparent. "She wants to keep the cats. Every time an animal gets in here, she wants to keep it. I've told her time and again she can't have a pet."

"Why not?" said Donna, frowning. The Doctor withered her expression with one of his own.

"_Because_," he said with badly forced patience, "if I let her keep every animal that's ever managed to get in here, she would now be the proud owner of eighteen dogs, ten cats, four reptiles, forty-four assorted rodents, eleven primates and seven thousand, six hundred and nine variations on the theme of insect. Oh," he added sourly, "and one velociraptor."

"Um. Well," said Donna, after a decent interval, "that's me told...but it still doesn't explain how you're running around in circles. What's a pocket?"

The Doctor explained about four dimensional relativity and how the TARDIS could shape the continuum with impunity. He spoke at length about pinched spacetime and subdimensional curvature. He waxed rhapsodic on the subject of quantitative phase adjustment. He would have elaborated upon the finer points of non-Euclidean tangential geometry but for the fact that at that point, Donna threatened to punch him.

"It's a bubble in space," he told her, lamely. "It's perfectly self-contained, just very small. If you go more than twenty metres in any direction at all, you'll end up right back where you started."

"That's impossible," said Donna. The Doctor shot her a brief but meaningful glance that spoke volumes about his feelings regarding the word 'impossible', and then regrouped.

"Not for the TARDIS," he said, firmly. "She does with time and space what you used to do with Lego as a kid, believe me."

"You mean she makes half a house with no windows or doors, and then gives up and starts crying because the plastic tree's broken and all the people look scary because they've got no hair?"

There was a very long, luxuriant silence; the kind of silence that is very rare in mortal realms, and is only rendered possible because two people are staring at one another in an unbreakable deadlock of bewilderment. The entire universe shuffled its feet awkwardly.

"Right," said the Doctor, carefully. "The Archives, then?" He made as if to set off, then paused and glared meaningfully at the sky. Donna felt a very faint sensation of pressure on her middle ear, and then it was as if the garden had _twisted_ around her. By the time she managed to shake off the peculiar aftershock of this, the Doctor had crunched off down the path.


	2. Chapter 2

"That's it," said the Doctor, savagely. "She's grounded for a month."

The Archives weren't a place that Donna normally cared to visit. She'd been badly spooked on her first visit when she'd got lost amongst the endless ranks of cupboards and shelves, and hadn't been back since. Now, however, it was looking a lot more interesting, if no less chaotic.

There was no sign of the books, papers, and other media that had previously colonised the place like a flock of mouldering bats; they had been replaced by endless rows of cat-related paraphernalia. Donna saw a wicker basket full of fluffy balls on one shelf and, beyond that, gleaming tins of Whiskas piled five high. The floor was littered with saucers of cream at which more than three dozen cats of all shapes and colours were drinking peacefully, completely oblivious to their presence.

"We need to find the point of entry," the Doctor was saying. Donna, who had been hypnotised by the sound of synchronised lapping, dragged her attention back to reality – or, she amended mentally, whatever passed for reality in a room that was rapidly filling up with time-travelling cats.

"What?" she managed, vaguely. She watched a gorgeous silver Persian nearby finish its meal and stroll off, plumed tail swaying gently. The empty saucer, meanwhile, popped out of existence and was promptly replaced by a full one.

"There's got to be a rift in spacetime where they're getting in," he said. " I did warn you; it's like a cat flap. Once one finds the way in, the others won't be far behind."

He snorted angrily and set off down a randomly chosen aisle, picking his way through the feeding animals, most of which ignored him completely.

_Sploop._

"Doctor?" called Donna, although hesitantly. The noise had been very faint, and even now she was beginning to doubt she'd heard it at all. Already halfway around a distant corner, the Doctor poked his head back into the aisle and frowned at her.

"What is it?"

Donna looked around wildly and tried to pinpoint the source of the noise as the Doctor sighed harshly and started to make his way back through the minefield of preoccupied cats.

_Blort._

This time she had it. She reached out and grabbed the Doctor's elbow and aimed him at a nearby closet.

"There's something in there," she hissed, and urged him forward.

The Doctor reached out gingerly, and somewhere on the fringes of realisation it occurred to Donna that they were being watched. She risked a half-turn of the head, and saw that every cat in the Archives had stopped what it was doing and was watching the Doctor as he inched forward.

Donna drew and held a deep breath. Eighty-four cats flicked an ear apiece. The Doctor turned the handle.

There was a rather fitting pause – and just enough time for his eyes to widen in horror – before he was deluged with cats. Donna back-pedalled as the feline tsunami rolled towards her, spitting and wailing, and as she did so, she saw the Doctor's hand waving helplessly from beneath a pile of highly irritated fur.

The wave broke almost at once and the cats fled. Donna stepped away from the wall and knelt down by the semi-conscious Doctor, who was slumped against the closet door and moaning feebly. There was a black kitten curled up on his head.

"Wstfgl," said the Doctor. Donna reached out and removed the kitten, setting it on the floor and gently shooing it away.

"I had one of those once, but the end fell off," said Donna, trying to lighten the mood. She reached out and slapped his cheek, gently. When that failed to produce the desired response, she applied a little more force.

"_Ow!_"

"Sorry," said Donna, brusquely, "but we can't sit around all day, can we? We've found out where they're getting in. What do we do now?"

The Doctor declined to answer. Instead, he struggled to his feet, made a very futile attempt to brush the cat hair off his suit and set his jaw.

"Look," he said, and pointed at the back wall of the closet. Donna squinted into the gloom. What she had taken at first to be a random pattern in the grain of the wood was in fact far more interesting. A section of the wall was distinctly puckered, and as she watched, it pulsed briefly before opening with a soft _blup_ and ejecting a scrawny ginger cat, which blinked myopically at her before hopping smartly off the shelf.

"That," said Donna, eventually, "is quite possibly the most unpleasant thing I've ever seen."

The Doctor withdrew the sonic screwdriver and aimed it at the hole, which was already quivering again. There was a startling flare of light and an unexpected, high-pitched whine, like acoustic feedback. Donna's ears ached, and she pinched the bridge of her nose in an attempt to clear the sudden imbalance. When the sensation of pressure had faded, she opened her eyes and saw that the hole was sealed.

"Is that it?" she said, cautiously?

The Doctor stared at her for long seconds, as if he'd never seen her before. Then, very slowly, he turned his head and looked at half a dozen suddenly very nervous cat faces, peering at him from behind a bookshelf.

"Not yet," he said.

* * *

"Can you reach it?"

"No!"

Donna readjusted her grip on the base of the ladder and shoved it a few feet sideways. The wheels squeaked. At the top, the Doctor did the same and gripped a rung fervently.

"How about now?" she called up, wiping a hand across her forehead irritably.

The Doctor peered into the foetid darkness atop the shelves and pursed his lips, clucking gently. The cat half closed eyes like twin fire opals in the gloom and gave him a fairly typical cat look; namely, the one designed to convey: _I'm quite happy where I am, thank you so very much indeed, and if you even think about trying to move me you're going to be taking a short course in skin grafts._ To give him due credit for common sense, the Doctor hesitated for a second, and then shrugged wearily.

From her position at the bottom of the ladder, Donna couldn't see what was going on, although she managed to form a reasonable guess in the aftermath of what happened next.

There was a soft snarl, followed by an unidentifiable organic noise, and then a flurry of claws on wood. The universe held its breath, and when it exhaled the Doctor came skidding down the ladder at high speed, leaving a red smear all the way. He scowled at Donna for no good reason before smacking his maimed hand into his armpit with a slight whimper.

"Here, let me see," said Donna firmly, and grabbed his wrist. There were four neat slashes across the palm of his hand, punctuated with bright beads of blood. She cringed. The Doctor merely snorted and retrieved his hand, cradling it awkwardly.

"Little sod," he said, absently.

Donna glanced around and up. The cat, seemingly confident of a battle won, had not gone far; it was lounging bonelessly atop of a shelf marked 'Y:CH-ZzzT' and twisting its tail into delicate sine waves. She frowned fiercely and wheeled the ladder along the shelf towards the insolent animal. Even from that distance Donna could hear it purring, which seemed to her to be unnecessarily sarcastic.

"I wouldn't do that if I were you," sighed the Doctor from behind her. She glanced over her shoulder for a second. The Doctor raised his hand long enough to remind her of his battle scars and cocked a questioning eyebrow.

"Look, I'm good with cats, okay?" said Donna firmly. "You, on the other hand, don't strike me as a cat person at all. No offence," she added.

"None taken," said the Doctor, in tones glazed with irony.

Mollified, Donna clambered up the ladder and raised her head cautiously over the parapet on the edge of the top shelf.

The animal was gone. In its place there was another trembling, puckered hole, almost identical to the one that had spat out the cat in the first place. Donna stretched out a hand, fingers shaking slightly, and traced the edges of the hole.

"Really, really don't do that," said the Doctor. She paused, and drew back her hand.

"Why not?"

"Well," said the Doctor, after a decent pause for effect, "there are several fundamental reasons, but I think the most vital is that you really don't want to be poking your hand into a hole that could lead anywhere – and I do mean anywhere."

"So where's the cat gone?" said Donna, exasperated, stepping back down the ladder.

The Doctor merely shrugged.

"Search me," he told her. "Only he knows. The point is that they can control the tangent of travel within these wormholes. You, however, can't, and I don't want to have to explain to your mother that you lost your hand somewhere in the Early Silurian period. Will that do?"

Donna was about to reply, when there was a startling boom that scythed out through the Archives and rang like a dropped coin through the stifling air around the shelves. Donna tried to flinch away from the sound, but it seemed to her that in defiance of conventional physics, it was coming from everywhere, down to and including her own inner ears. The entire room resonated with it. Her eyeballs ached. Her teeth set themselves on edge in sympathy. When she swallowed hard and opened her eyes again, she saw that the Doctor looked ashen.

"It's the Cloister Bell," he said, huskily. "It only rings when there's trouble."

"Define 'trouble'," squeaked Donna, through a rapidly closing throat.

"Try the end of the universe," said the Doctor flatly, and then ran for it.


	3. Chapter 3

Donna skidded to a graceless halt in the Cloister Room, and almost slammed into the Doctor's back. Recovering with commendable speed, she looked around and then up, and lost her breath once more.

The room was lit by a massive crystal dome containing millions of intricate triangular facets, which let onto a twilit sky dominated by a stately, turning galaxy. As Donna stared at it, slack of jaw, she saw a supernova twinkle briefly in one of the outer arms before it died away with shocking speed.

She finally dragged her gaze down and took in the rest of the scenery; beneath the dome were ranks of sharp Gothic arches picked out in wrought iron, each containing its own deep puddle of shadow, and in the middle of the room there was the Cloister Bell.

It was heavy and primeval, a study in decrepitude, with one evil scar running down its rusted black flank and a deep gouge in the rim. This debauched grandeur was offset by the fact that this gnarled monster hung, quite motionless, in an intricate cat's cradle of silver chain that looked – set against the weight of the bell – to be as fine as cobweb.

The tolling, Donna was beginning to realise, was approaching tolerable in here, and she wondered how that could be so when they were standing less than a dozen feet away from the bell itself. She sidled across the floor, heels dragging, and reached out tentatively.

Laying one hand on the great curve of the bell sent a shudder up her arm, into her brain and back down her spine on a hairpin bed. The iron was vibrating so gently that she had to press her fingertips hard up against it in order to feel it at all. It was far too soft a movement to be producing the sonorous peals she was hearing.

While Donna had been otherwise preoccupied, the Doctor had stepped up beside her. He was frowning fiercely.

"Something's not quite right here," he muttered, then bent at the waist and poked his head up inside the bell. After a few seconds, perturbed by the fact that he had not resurfaced, Donna joined him.

There were two kittens in there. One had all four paws wrapped around the clapper and was swinging it to and fro, bouncing off the inner curve of the bell with every sign of enjoyment writ large across its pinched, cross-eyed little face. The other, which looked to be egging its companion on, was perched on the narrow inner lip of the bell. It glanced over at its audience, and set to washing itself with a surprisingly credible air of innocence. The Doctor sighed heavily, reached out and plucked them both up.

He then straightened up and paused visibly.

Donna stared as the Doctor weighed a kitten in each hand, preoccupied, almost as if he were trying to decide between two bunches of bananas in the supermarket. He narrowed his eyes at one and lifted the other; they opened little pink mouths and mewed at him in perfect sync. She watched a smile dawn on his features.

"Of course," he murmured, then rounded on Donna and held the animals out triumphantly, the smile transmuting all at once into a wild grin.

"One of them's just widdled down your sleeve," she told him. He apparently ignored this.

"Look at them!" he insisted. Donna subdued her irritation and studied the kittens. Both were patterned with black and white blobs, and had one endearing wonky ear apiece, although one kitten's was on the left side and the other's was on the right. She couldn't see anything out of the ordinary, and scowled up at the Doctor in an effort to convey this.

"It's the same kitten," he explained, "except they're mirror images. What do you know about quantum theory?"

Donna snapped.

"Strangely enough," she began, pouring sarcasm like hot custard over each syllable, "not a lot. I think I was ill the day we did quantum theory in bleedin' primary school! Now what are you waffling on about, please?"

The Doctor, by way of response, merely handed her a kitten. It did not escape her notice that it was the damp one.

"Think proton and antiproton," he said, firmly. "When those two particles meet, they both vanish. Watch carefully," he added, and before Donna could speak, he had moved his kitten up alongside hers so that they touched. There was a startling flash of pure white light, and when her eyes had cleared themselves of the more bizarre after-images, she looked down to see that both animals had completely disappeared.

"Cat and anticat!" said the Doctor, gleefully.

* * *

The Doctor hared down the corridor in pursuit of a small pack of ginger cats. They skidded around the corner, tails held aloft like quivering flagpoles, but when he turned the corner himself, they were gone.

Behind him, a bright flash erupted from a doorway. He half turned.

"Got one?" he called, irritably.

"No," came Donna's slightly muffled reply. "I'm taking a picture."

"Why?"

"You should see what this lot are doing," said Donna, cryptically.

"Just get on with it, please," said the Doctor, seizing a huge breath. When he looked back, the cats were watching him carefully. He released the breath, slowly and gently, and made a sudden grab for them.

This turned out to be both a very good and a very bad idea. He managed to secure a hold on two of the cats; however, while he had been doing this, the others had decided to launch a counter-offensive. As the Doctor lifted his captives, he became aware of an odd sensation around the toes.

He looked down to see several more cats gnawing on his sneakers. Three were going straight for the shoes, while a fourth had seized upon a stray shoelace as the grand prize and was tugging ferociously at it as if it were a recalcitrant worm.

Snarling, the Doctor dispatched the two he was holding and then bent double like a pinstriped flamingo, grabbing for his attackers, which promptly scattered. He set off after them – and would have made a fine job of it were it not for the trailing shoelace. By the time he'd scrambled to his feet and made an attempt to straighten out his nose, they were gone.

Donna, meanwhile, pocketed her camera and picked up two more cats from the pile in front of her. They regarded her incuriously and stuck out twin pink tongues. Satisfied by this, she brought them together and squeezed her eyes shut as the actinic flare consumed them.

When her vision cleared, she glanced down. One cat remained, and it was curled up at her feet, sides rising and falling infinitesimally, tail curled about and tucked neatly beneath its soft pink nose.

Donna sighed and turned her head, looking for its opposite number, but they were quite alone in the room. She looked back down again; the cat continued to sleep, and one ear vibrated ever so slightly in the midst of a dream.

She knelt down and studied the animal at closer quarters, and it was only now that a sense of familiarity began to creep over her. She stretched out a hand and ran idle fingertips through the dense tabby and white fur, running them up through the silky hairs until she located something she had not so far found on any of the other cats.

It was a collar. Pushing the fur aside, Donna could see it was a purple velvet collar with little fish embroidered on it in silver thread. The sense of familiarity grew heavier and more involved, and was now joined by a distant memory, so vague that she could only link it to this collar.

Her fingers strayed further; the cat shifted in its slumber, but otherwise reacted no further than to squeeze its eyes shut even tighter. At last, Donna found the small brass disc attached to the collar, gripped it delicate between finger and thumb and turned it around so she could read the engraving.

She read it two more times, just to be sure.

Her puzzled half smile, which had been fading steadily, vanished altogether.

Then she gathered the snoozing cat into her arms and set off in search of the Doctor.


	4. Chapter 4

The console room was full of fish.

It seemed to the Doctor that this was a slightly flippant observation, since it was by no means an hyperbole; the spaces beneath the console were crammed with salmon, the rafters festooned with sardines, the decks laid with drifts of slippery whitebait and every crevice in the walls packed with glossy pink tuna steaks. He saw his work, and saw that it was good.

Brushing his hands gleefully, he hunkered down behind a pile of rainbow trout and, trying to ignore the distressing odour about the place, settled down to wait.

It had not been more than a few minutes before one of the piscine mounds near the far door shifted and dislodged a black cat, which was already gripping a small halibut in its jaws with the expression of an animal that means to keep on gripping. It surveyed the room with disdain, then settled beneath a nearby panel and began to eat.

Minutes passed, and more and more cats filtered into the console room. One or two minor fights broke out, but since there were several hundred fish for each cat present, they soon dissolved into embarrassed preening and half hearted hisses.

The Doctor peered through a gap between two dorsal fins, narrowed his eyes, and counted. When he was satisfied, he reached out, without looking, and groped for the button that would seal the doors.

Before he could do so, however, Donna stepped through into ankle-deep flounder. She looked down and then back up again with a nonchalance that only eight months of travelling with the Doctor could bestow, and then frowned at him.

"You can come out," she said, quietly. "I know why they're here, and I know how to get them to go away."

The Doctor was so surprised by this that he bounced up from behind the wall of fish. He opened his mouth for a second, looked thoughtful, then closed it again and rooted in his pocket. Only after he had removed the sardine did he refocus on Donna and, more importantly, the drowsy bundle in her arms. He frowned quizzically.

"Isn't that..."

"Yes," said Donna, hugging the cat to her. "It's the first one. This is why the others showed. She's in season."

"How d'you know that?" asked the Doctor, although Donna watched a subtle expression flow across his features that suggested that he already knew the answer.

"I know because this is Sweetheart, and she's my cat."

The Doctor, to give him his due, simply nodded sagely.

"How long has she been missing?" he said, not taking his eyes off the contented animal, which shuffled in Donna's arms and purred like a distant chainsaw.

"Thirty years or so," said Donna, with a small shrug.

"Only from your perspective," said the Doctor absently, now almost totally lost in thought. "Give her here. I want to find out what happened."

Reluctantly, Donna handed over her charge, and the Doctor sat down on a handy step with the cat sagging happily across his lap. He chuckled softly, then took its head between his hands and concentrated. His breathing slowed and roughened, quickly becoming hoarse and soporific.

Donna had taken up station behind his shoulder, and now she watched as the cat's eyes widened, pupils dilating until the animal's soft yellow irises were almost lost to view. The steady purr also deepened, becoming throaty, and slowed until its rhythm matched that of the Doctor's breathing.

"Okay," said the Doctor, his voice jagged, and sounding as if he were speaking through several layers of cloth. "She was in the garden...she heard you calling, but all of a sudden, there were other cats."

"Males?" said Donna, quietly

"Yes," breathed the Doctor, still lost in the cat's glossy eyes. "They chased her. She couldn't find anywhere to hide. She panicked. Did the only thing she could. She slipped through spacetime."

"She's a Schrödinger Cat?"

"Half Schrödinger Cat," said the Doctor, as the cat's ears flickered. "A dormant gene; it only came into play when she first came into season. No wonder she didn't know how to handle it..." he hesitated, and all of a sudden, his back stiffened. "Okay, that's not good. Looks like she ended up in Australia first of all. She's wondering what to do about the enormous rats.

"She's jumping again, and this time...what's that? It's dark. Looks like a rhino. Is she in Africa? I...ah, no," he muttered, grimly, "it was the horn that confused me. It's a triceratops."

Donna gaped, and drew breath, but the Doctor was already continuing.

"She's in the void now. Trying to pick an exit, but there are too many. She's looking for a trace of you...there!" he cried, suddenly all exuberance, but still not breaking eye contact with the cat. "She found you. We were passing by. She didn't know how much time had passed for you, though. She jumped, but while the door was open..."

The Doctor exhaled loudly and harshly and released his delicate grip on the cat. Free of the trance, it nuzzled his hand lovingly, whiskers pricking and flexing with delightful abandon.

"We can take her home," said the Doctor, craning his neck to catch Donna's eye at last, "but it's up to you. If you want to keep her, we can do that, too."

There was a long, and very long pause. Donna felt the universe expand just a little further towards infinity, and it tickled the back of her neck, as if she felt she were being watched. Finally, she shook her head.

"No," she said, firmly. "I miss her now, but I missed her even more when I was little. Let's take her home."

The Doctor nodded and broke his gaze, bouncing to his feet, running both hands through his hair until it looked even madder than usual.

"The seventeenth of August, 1975, then," he said, brightly. Donna recoiled as if she'd been smacked.

"How do _you_ know that?" she demanded.

"I don't," said the Doctor, already preparing the console. "She does," he said, and angled his head at the cat. Then, without waiting for any further response, he slapped at a lever, and the TARDIS twisted into a handy crack in the fabric of the universe.

When her eyes had stopped rotating in their sockets, Donna shook her head and saw, first of all, that the fish had gone. Even the smell of fish had gone, which she considered was a minor miracle even for the TARDIS; it was one of those smells which somehow contrived to crawl into the nostrils and camp out there until forcibly ejected.

The second thing she noticed was that the cats were clustered around the door, staring up expectantly, eyes wide. The Doctor picked his way through the furry minefield and opened the doors. There was nothing out there but blackness, although a painful ache in the back of her retinas told Donna that this was not simply due to a lack of light, but due to a lack of reality.

"Everybody out," said the Doctor, not menacingly, but with an edge to his voice that hinted at future menace, depending on circumstance. The cats rose and, in pairs, trotted out into the nothing. Donna picked up Sweetheart once more and ran distracted fingers through the cat's fur, but otherwise watched in silence until the last wavering tail had vanished into the sucking blackness outside the TARDIS.

The Doctor shut the door behind them, and heaved a hearty sigh of relief. Then, hand still on the latch, he counted to fifteen under his breath while Donna watched, baffled beyond endurance. She was just about to interrupt this bizarre deliberation when the Doctor raised a cautionary hand and dragged the door back once more.

It was the scent that hit Donna first, carried in through the door on a warm, pleasant breeze. It hadn't been a part of her life in many years, but the scent brought the memory straight back at once. There had been a magnolia tree in their garden when she was small, and she could smell it once more. The sensation ran down her spine and into her feet, and she took a step forward.

The door slammed. The Doctor, who had been standing a little too close, leapt back a full six inches. His eyebrows knotted, and he craned his neck at the ceiling.

"You _can't _keep her," he said, firmly, and wagged a finger for emphasis. "She's not yours, and besides, she..."

"Doctor," interrupted Donna, softly, "it's all right. I'll handle this." She took an even breath, then looked up.

"I love her too," she said, eventually, despite addressing her voice to what – had she not known better – would have felt like thin air. However, she sensed a tiny change in the air pressure, and understood that the TARDIS was at least paying attention.

"I want to keep her too," she went on, "but it's not fair." Donna paused and cast a glance at the door, but it remained closed.

"You don't have to do it because you were told," she said, cocking her head at the Doctor, "but you can always do it because it's the right thing to do. How's that?"

No response. If anything, the door seemed to huddle against the frame.

At that moment, the cat wriggled insistently in Donna's arms, snaked out from under her elbow and dropped to the floor on four soundless feet. It curled its tail questioningly, first one way and then the other, and looked back over its shoulder at Donna for one long, one very, very long moment in time. Donna rubbed at her eyes with the back of her hand, but nodded.

"See you soon," she whispered.

The cat paced across the floor and reared up on its hind legs, placing pink pads against the door of the TARDIS. It tilted its head and gave a soft, querulous, "meep", and at this, the door finally swung back in silence.

The breeze rushed in once more, this time carrying with it not only the heady scent of the magnolia, but also the soft refrain of a young girl's voice; not afraid, but sounding a little concerned.

"_Sweetheart? Where are you? Come here, girl_."

Donna opened her mouth and started to move, but the Doctor frowned at her and laid a finger across his lips.

"_Come on, girl_," said the distant voice once more, "_time for dinner._"

The cat looked back at Donna once more, but this time there was no sad query in its gaze. It blinked carefully, turned about once more, and slipped out into the hazy summer night.

The Doctor closed the door behind it and exhaled gratefully.

"That's all sorted, then," he said, cheerfully. "Where to now?" Donna, returning to reality with a thump, her eyes rimmed with pink, gawped at him in frank disbelief.

"Sometimes," she said, her voice winding up, "you can be the most arrogant, insensitive, egotistical..."

"Stop, you're making me blush, said the Doctor, ramming his hands in his pockets and grinning.

"So where are we going now?"

"Sorry, isn't that what I just asked you?"

"I don't know. Wherever. Atlantis?"

"You didn't pack any wellies."

"I mean _before_ it started sinking, you dumbo."

"Oh good grief, stop being a pain and let's just hit Random, okay?"

He pressed the button.


End file.
